1. Technical Field
This invention relates generally to fuel gauging for rechargeable battery packs, and more specifically to a method for estimating the time remaining until a rechargeable battery pack is fully charged.
2. Background Art
Many portable electronic devices, like cellular telephones, laptop computers, pagers, radios and personal digital assistants (PDAs), rely upon rechargeable batteries for their portability. These batteries provide energy while on the go, but must be recharged once the energy is depleted.
Some electronic devices include fuel gauging circuits that attempt to display the amount of energy stored within the battery. For example, some devices include a display with a little picture of a battery on the screen. As the rechargeable battery stores energy, the battery picture slowly changes from transparent to colored. By looking at the amount of the battery picture that is colored, a user may roughly estimate how much energy is stored within the battery.
The problem with these systems occurs during charging. By looking at a graphical fuel gauge, a user can not tell how much longer it will be before the battery is fully charged. Imagine a police officer who wants to take a fully charged radio out on the beat. If he looks at a graphical fuel gauge and sees that his battery is roughly three-quarters charged, what does this tell him about how much longer will it be before the battery is fully charged? Will it be another 20 minutes? 30 minutes? The answer is that he can not tell based upon presently stored energy alone.
There is thus a need for an improved fuel gauge that tells a user how much time is remaining until a rechargeable battery is fully charged.